Most automated mechanical systems developed today are built as unique custom one-off systems employing little or no standardized architecture. This one-off design methodology tends to result in systems exhibiting relatively high cost and a low rate of change and diffusion of new technology.
Another undesirable effect of custom mechanical design methodology is rapid obsolescence. In general, operator interfaces are cumbersome, maintenance training is complex, and the logistics trail for maintenance is a permanent and expensive user obligation.
Often, the designer of an automated mechanical system is first faced with the design of a machine joint, which, owing to the relative absence of standardized machine joint solutions, must be performed beginning from basic structural components, such as plates, beams, and bearings.
Given a machine joint of sufficient rigidity, the machine designer then moves to specification and selection of a prime mover, a power source for the prime mover, positional and velocity feedback sensors for the joint, a control system for the prime mover, all necessary wiring, and any necessary intermediate geartrain and power transmission elements. Generally, these components will be discrete components. Although certain components may be designed to interface with the related components, a relatively high degree of engineering effort must still be exerted to ensure that the various components will work together properly under a variety of operating conditions.
One area in which integration has been effectuated with some degree of success is integration of the prime mover and the gear train. Modules incorporating both a prime mover and a gear train are known as “gearmotors” or “gearhead motors.” Although somewhat successful, this integration has suffered from the use of inadequate gear train designs, thereby limiting the overall effectiveness of such modules.
Development work in gear trains has been largely stagnant for many years, with the conventional wisdom being that all the science available has borne all the results that are feasible. Generally, system designers would prefer to eliminate the gear train entirely, along with its weight, backlash, noise, cost, and presumed complexity.
Hypocyclic gear trains were first developed and patented in the late nineteenth century. A further surge in patenting occurred in the mid-1930s. Several industrial manufacturers presently produce gear transmissions using hypocyclic gear trains, but their designs mimic older designs, which contain many parts and bearings, a circuitous force path, and two opposing wobble plate gears, for balancing purposes. The balancing issue has limited, to a certain extent, the use of wobble gear designs, but so long as the driving eccentric for these gears is relatively small, on the order of 3% or less, they can be well-balanced using modern methods of precision balancing.
In some hypocyclic gear trains produced presently, only one wobble plate gear mesh is used. These designs use pins through the plates to transmit torque to the output plate, adding a further level of complexity and a number of dimensions having critical tolerances.
For perhaps thirty years, a low level of interest has been shown in the design of hypocyclic motors with the claim that they produce high torque at low speeds. They do, but no one has heretofore found a satisfactory means to get that high torque to a concentric rotating output shaft.
At least three principal variations of cycloidal drive gear trains currently exist. These include the designs produced by SUMITOMO™ (Japan), TEIJIN SEIKI™ (Japan) and ANDANTEX™ (France). These designs all depend on dual wobble plate differencing gears, set 180 degrees out of phase for balancing, driven either by a precision cycloidal surface or a dual set of eccentrics. The force path for these devices between input and output is long and circuitous, requiring a large, and very heavy, hoop structure to keep all the forces contained.
These devices use rollers on curved surfaces and cantilevered pins to provide the final drive to their output plates. Also, this type of drive is connected to a small output shaft supported by additional bearings. All of this adds considerably to the compliance and lack of rigidity of the gear train. Because of their unique geometry, complexity, volume and weight, these gear trains are very difficult to integrate into self-contained actuator modules.